1. Field of the Invention
The present invention relates generally to medical devices and, more specifically, to implantable medical devices that include telemetry capabilities.
2. Description of the Related Art
There are a wide variety of implantable medical devices (IMDs) that sense data and/or provide therapies. In the cardiac arena, there are implantable loop recorders (ILRS) that are implanted subcutaneously to record cardiac data. So called “low power” devices provide pacing therapies and are often referred to as implantable pulse generators (IPGs) or pacemakers. “High power” devices provide cardioversion and/or defibrillation therapy and are referred to as implantable cardioverter/defibrillators (ICDs). ICDs will often also having pacing capabilities and, as used herein, may take either form. Many other types of cardiac devices are available and, of course, implantable devices are useful in many other contexts such as neurology, diabetes, and pain management, to name a few. While particular reference is made to ICDs for illustrative purposes, it should be appreciated that the present invention is not so limited and applies to a wide variety of implantable medical devices.
A typical ICD or IPG is implanted having a non-rechargeable battery with an expected lifetime of 3-15 years, with 5-10 years being most common. This has been made possible with advancements in battery and capacitor technology, as well as reducing power requirements of the components within the device. At the same time, many more features, therapies and capabilities are provided in modern IMDs that simply require additional power. Therefore, with these considerations in mind, power management is an important aspect in the design and manufacture of IMDs.
IMDs have had telemetry capabilities for quite some time. In the past, a programming head having an inductive coil was placed in contact with the patient's skin proximate the site of implant. Data was transferred between the programming head and the IMD through inductive coupling over this very short distance. The programming head was connected to a device such as a medical device programmer that was able to receive and display data from the IMD as well as program various functions of the IMD.
Recently, there has been a trend to move to so-called “distance telemetry,” wherein the IMD communicates with an external device via radio frequency communication. This permits communication with the IMD without requiring the presence of a programming head during the communication session. In-office follow-ups are easier and less cumbersome, but this also permits a patient's IMD to communicate in virtually any environment without encumbering the patient. For example, a patient may be provided with a home monitor that communicates with the IMD via RF communication, and transmits this data to a central server (e.g., the Medtronic CareLink™ database). Similarly, the IMD may communicate with any number of external devices in this manner.
While providing many benefits, distance telemetry also utilizes scarce power resources. This is a consideration both in transmitting data as well as when “listening for” and actually receiving data.